The advanced state of the art of electronic devices is apparent from the diversity of the functions and good performance of such devices, particularly in view of their small size. The state of the art is typified by large scale integrated circuit devices (LSIs). The preferred embodiment of the present invention is especially suited for testing LSIs. An LSI or other device being tested is referred to herein as the device under test, or DUT. The invention can also be used for testing smaller scale integrated circuits and individual parts such as transistors, FETs, resistors, capacitors, inductors, etc.
A feature of modern LSI technology is that components that used to be peripheral circuits of such LSIs are now incorporated into the LSIs to expand their function and increase their speed. As a result, input/output signals of LSIs include direct current (DC) signals, digital signals and analog signals. The time relationship between the various input and output signals may be either synchronous or asynchronous, and their signal modulation speed may be greater than 100 MHz. These input/output signals are referred to as the mixed signal in the description of the preferred embodiment.
Conventional LSI testing devices are often realized by extending known IC testing devices or following the concept of known IC testing devices; as a consequence, testing of LSIs has involved dividing the LSIs into individual functional blocks. For example, for a functional block dealing with digital signals, a test similar to that performed by a digital IC tester has been used and for a functional block dealing with analog signals a test similar to that of an analog IC tester has been used. An LSI that passed all functional block tests was judged to be a conforming article. Such a "divide and govern" test methodology may be effective in a case where each functional block is highly independent, but when the blocks are somewhat interdependent, which is the case with recent LSIs, that methodology cannot adequately test how the DUT would perform in an actual use environment.
For example, one cannot evaluate the performance of a high speed analog/digital converter (ADC) in an actual use environment by just evaluating its DC input/output characteristics. The relationships between the input signal frequency and the conversion error and the input waveform and the conversion error, and the mutual relationship between the input waveform and the conversion clock and the conversion error, are characteristics that should be determined for an actual environment.
Moreover, in an interface IC for communications, while input/output is carried out asynchronously, data is input/output from/to a synchronous digital circuit and sometimes the input/output signals include analog signals.
A digital filter also contains analog input and output circuits and an internal digital circuit which are connected via an ADC and a digital/analog converter (DAC). In this case, characteristics of the transfer function that depend on the relationship between input signals and an internal clock, noises and spurious characteristics have to be evaluated.
Moreover, when an LSI on which a feed-back circuit should be externally equipped is tested, a control input has to be calculated and supplied immediately after measuring and evaluating an output signal; e.g., when an excessive input is detected in an ADC, the attenuation of a pre-attenuator must be increased.
Another problem with prior art testers is that calculation speed decreases when the outputs of individual pins are mathematically combined and the calculation result is used for evaluation. For example, in a tester wherein each signal generating and signal measuring module, or a signal generating and signal measuring shared module (hereinafter simply referred to as a GM module), and a signal processing module are connected through the intermediary of a memory, the processes of storing data into the memory, calculating results, storing results and outputting results are carried out, making it difficult to make calculations in parallel. Moreover, communications between the GM module and signal processing module must rely on the intermediary of a host processor or on sequential communications of a signal processor, which slows the operating speed of the tester and causes the programs for such procedures to become extremely complicated.
Accordingly, a goal of the present invention is to provide a testing apparatus for testing electronic devices that have mixed input and output signals, thus simulating an actual use environment of such devices.